This investigation attempts to determine the relative contributions of sensory and nonsensory factors that underlie cyclic variations in pain thresholds across the phases of the menstrual cycle. Three groups of subjects (menstruating women, women on contraceptive pills, and men) will rate their perception of various intensities of radiant heat stimuli in twelve successive sessions. The data will be blocked into the phases of the menstrual cycle (menstrual, postmenstrual, ovulation, and premenstrual) and a relative operating characteristic analysis (ROC) will be performed. The ROC analysis is a better technique for pain research than the traditional threshold estimation procedure because it allows an experimenter to measure the observer's ability to discriminate the presence of a sensory event, independent from response bias effects such as attitude and experience. Applications of this research to the treatment of dysmenorrhea and to the concept of "premenstrual syndrome" will also be addressed.